Non-volatile memory (NVM) has pervaded many of the devices that we use each day, from the music of MP3 players, to the photos on digital cameras, to the stored e-mail messages in our smartphones, and to the files that we carry in our portable devices.
With the different NVMs in the current market, a phase change memory (PCM) NVM has made rapid progress in terms of sophisticated demonstrations of scaling to small device dimensions. The PCM typically exploits large resistance contrast between its amorphous and crystalline states in so-called phase change materials. The amorphous phase tends to have high electrical resistivity while the crystalline phase exhibits a low electrical resistivity, sometimes 3 or 4 orders of magnitude lower. Due to this large resistance contrast, the change in read current is large enough to open up an opportunity for multiple analog levels in the programming of the PCM.
Currently, prior to any programming pulse that is applied to the PCM, a separate read operation is performed in order to determine whether a further programming pulse is required. Typically, the separate read step may take about 50 nanoseconds to perform and the programming pulse step another 50 nanoseconds. The total operation taking about 100 nanoseconds.
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